1. Field of the Invention
The present invention relates to an electrophotographic copying apparatus comprising a belt-shaped photoconductor member provided with a photoconductive layer, which is cleaned with a magnetic cleaning member having an improved cleaning efficiency, thereby attaining extended life of the belt-shaped photosensitive member.
2. Discussion of Background
In recent years, the practical application of electrophotography to printers for office copying machines and for various types of data processing terminal devices, including data transmission systems for facsimile and the like, and also for printing systems, has developed rapidly because of the simplicity of the systems, the high speed of data handling and the high quality of the images produced.
The electrophotographic copying apparatus which forms images basically uses an electrophotographic photoconductor comprising an electroconductive support and a photoconductive layer formed thereon. The electrophotographic copying process is as follows:
First, the surface of a photoconductor is uniformly charged by means of a charging device, and light which is modulated with respect to time and space to correspond to the data to be recorded in image form is directed onto the surface of the photoconductor so that an electrostatic charge pattern corresponding to the data, which is referred to as the latent electrostatic image, is formed. A corona discharge device utilizing a comparatively simple and stable corona discharge is generally used as the charging device. The electrostatic charge pattern is then developed using colored, charged toner particles, which may be simply referred to as the toner. Specifically, the toner is deposited on the surface of the photoconductor through the attraction or repulsion of the charged toner particles, so that a visible toner image is formed to correspond to the electrostatic charge pattern. Following this, the toner image is transferred to a recording medium such as a transfer sheet or the like. The transfer is generally implemented by providing, on the transfer paper, a corona charging of a polarity opposite to the polarity of the charged toner. The transferred toner image is fixed on the surface of the transfer sheet by some means such as by the application of heat or the like. On the other hand, the untransferred toner and a very fine paper dust which comes from the transfer sheet remain on the surface of the photoconductor. This mixture of toner and paper dust on the surface of the photoconductor is a drawback because when the next data is recorded, streaks and spots from this source occur on the image. It is therefore necessary to remove this toner and paper dust from the surface of the photoconductor using a specified cleaning member.
In a conventional cleaning method for removing the residual toner and paper dust from the surface of the photoconductor, (i) a blade made of a high molecular organic rubber such as urethane or the like, which is brought into pressure contact with the surface of the photoconductor, or (ii) a fur brush which comprises a metal roller made of, for example, aluminum, and nylon fibers which are fixed to the surface of the metal roller by use of an adhesive to form a brush thereon, which are rotated in contact with the surface of the photoconductor, is employed.
In this conventional cleaning method, the cleaning member, such as the blade or the brush roller, is pressed against the surface of the photoconductor by a mechanical means only, so that in the case where the photoconductor is in the form of a belt, it is difficult to press the cleaning member uniformly against the surface of the photoconductor. Because of this problem, there is a tendency for some parts of the photoconductor to be unsatisfactorily cleaned, and the deposition of toner on the background of the recorded image takes place.
As a method of eliminating these drawbacks, a method which enhances the cleaning effect is proposed in Japanese Laid-Open Utility Model Application 60-135757, in which a magnetic cleaning member with a built-in magnet, and a belt-shaped photoconductor provided with a magnetic member at the back side of the photoconductor are employed. In this method, the magnetic cleaning member is magnetically attracted to the magnetic member via the belt-shaped photoconductor, and therefore is pressed uniformly against the belt-shaped photoconductor.
The cleaning effect from using the method disclosed in the Japanese Laid-Open Utility Model Application 60-135757 is high in comparison with that obtained from using a method in which pressure is applied by mechanical means only. However, in this cleaning method, the undersurface portion of the belt-shaped photoconductor, that is, the electroconductive support portion, is abraded by the the magnetic member which is positioned on that undersurface of the photoconductor so that there is the problem that the particles formed by the abrasion from the electroconductive support scatter, and when the particles get between the belt-shaped photoconductor and the belt support and drive rollers, cracks appear in the photoconductive layer and white spots appear on the recorded image.
In the above method, the pressure applied by the cleaning member against the photoconductor can be enhanced. However, this pressure is not uniform in the width direction of the belt-shaped photoconductor, so that when a large number of copies are made, the problem of localized wear of the photoconductive layer occurs. When this type of localized wear occurs on the photoconductive layer, not only a drop in image density, but also toner deposition on the background of the image occurs, which is due to a localized drop in the initial development potential.
Furthermore the life expectancy of the belt-shaped photoconductor is shortened as a result of abrasion on the undersurface of the belt-shaped photoconductor, that is, the electroconductive support portion, and the wear on the photoelectroconductive layer.